Support File Upload for mobile

[qroac]

So far the upload component is only supported for web clients with a small placeholder component for mobile apps.

Would be great to have this feature on mobile platforms as well.
Maybe with two examples, one opening a file chooser and one opening the camera.

[RomanPeskov]

Thanks, that's a good idea. We have already implemented uploading files for mobile platforms with file chooser in the mobile-chat branch. So, in the near future we plan to add this functionality for mobile platforms in the upload module.